PROJECT SUMMARY This proposal describes a five-year career development program to prepare Dr. Ilanit Itzhaki for a career as an independent investigator. This program will build on Dr. Itzhaki's background as a stem cell biologist and experimental electrophysiologist by enhancing her knowledge base in sex hormones in cardiovascular health and disease and providing her expertise in molecular cardiology and medicinal chemistry for translational research in drug discovery and sex-specific therapeutics. Dr. Itzhaki will be mentored by Dr. Joseph Wu, Director of the Stanford Cardiovascular Institute. The proposed mentor is an expert in stem cell biology, pharmacogenomics, and drug discovery utilizing iPSC-derived cardiomyocytes (iPSC-CMs). To complement Dr. Wu's mentorship, Dr. Itzhaki will be co-mentored by Dr. Marcia Stefanick, Director of the Stanford Women & Sex Differences in Medicine Center, and an expert in the field of sex hormones and cardiovascular health and disease. The K99 phase of Dr. Itzhaki's training will consist of structured mentorship by the primary mentor and co-mentor, complementary meetings with the advisory committee, formal coursework, a provocative research project, and a program for career transition. For symptomatic long QT syndrome (LQTS) patients prone to life threatening cardiac arrhythmia, pregnancy can facilitate a unique period of anti-arrhythmic protection, when estrogen hormone level is at its highest. Deciphering the anti-arrhythmic contribution of estrogen can lead to the identification of much-needed new anti-arrhythmic therapeutic targets and the design of novel therapeutic entities. In the K99 phase of this proposal, Dr. Itzhaki will assess the effect of estrogen on arrhythmic propensity using female and male LQT patient-specific iPSC-CMs at the single cell and multicellular levels (Aim 1). Dr. Itzhaki will then identify mechanistic intracellular targets that facilitate estrogen's anti- arrhythmic benefit (Aim 2). The identified beneficial antiarrhythmic targets, will help guide Dr. Itzhaki in the R00 phase, in the design of an estrogen analogue, which will be assessed for sustained anti-arrhythmic benefits and absence of cardiotoxicity (Aim 3), with the intention of proposing new therapeutic entities that take advantage of hormone-based anti-arrhythmic benefits, yet at the same time allow the treatment of both male and female patients at all ages. Collectively, the insights acquired from Dr. Itzhaki's proposal can contribute significantly to the treatment of LQTS patients, specifically, and arrhythmia-susceptible congenital disease patients, in general, and promote the growing field of sex-specific therapeutics. Furthermore, using iPSC-CMs as a dish-to-bedside approach, to aid in the design of anti-arrhythmic therapeutic analogues and to serve as a high-throughput analogue-screening platform, will greatly contribute to the prospect of translational medicine. Finally, this work will provide a foundation for future studies using iPSC-CMs, as a human based patient- and disease-specific model, to interrogate the effect of sex hormones on cardiac arrhythmic propensity, to be eventually carried out by Dr. Itzhaki as an independent investigator. ! !